An Xyz Monster (pronounced ik-eez[1]) is a type of Monster Card that is colored black. They are stored in the Extra Deck. The card frame is also stylized by having it appear as if one is flying through space with many stars in the frame giving the appearance of one streaking by them and other stars appearing stationary due to relative distance (giving a realistic depiction of moving through space). According to Konami, Xyz Monsters are made of antimatter, and have traveled to Yuma's dimension from the other side of a black hole.[1]

Instead of a Level, Xyz Monsters have a Rank. This Rank determines the required Levels of the Xyz Materials needed in order to Xyz Summon your Xyz Monster. An Xyz Monster's Rank is depicted by a row of yellow stars in black orbs (as opposed to the yellow stars in red orbs of a monster's Level) that extend outwards from the left-hand side of the card (opposite to where a monster's Level would be depicted), similar to Dark Synchro Monsters. However, unlike Synchro Monsters, a Xyz Monster's Rank is not the total sum of the monsters' Levels used to Summon it; thus, if 2 Level 3 monsters are required, then the Xyz Monster would be Rank 3, not Level 6.

Most Xyz Monsters require you to "detach" (meaning "place in the Graveyard") their Xyz Materials in order for their effects to activate, limiting their effect usage. When an Xyz Monster is removed from the field, its Xyz Materials are sent to the Graveyard. Some also have negative effects when they have no more Materials attached, so it may be best to use such effects sparingly.

In terms of ATK, so far Xyz Monsters are not as strong as Ritual, Fusion or Synchro monsters. Few Xyz Monsters have more than 2400 ATK, those with 3000 or more ATK have either negative effects or rather difficult summoning requirements (High Level monsters or specific materials). However, Xyz Monsters are easier to Summon since they don't need a specific kind of monster (like a Tuner), a Spell Card (such as Ritual Spell Card), or a card to Fusion Summon (like Polymerization) Thus, there is little restriction in the monsters that can be used as Xyz Materials and can fit into almost any Deck.

In anime, during an Xyz Summon, Xyz Materials will transform into light entities, while coloured by their respective Attributes. Then, when the Xyz Monster is Summoned, its Xyz Materials will be floating around it as orbs colored by its Xyz Monster's Attribute.

LIGHT is yellow, DARK is purple, FIRE is red, WATER is blue, WIND is green, and EARTH is orange - each being a color of the visible spectrum. Some monsters when being used in an Xyz Summon that have the same attribute may have different color shadings.